Hitachi 7E300020, Технический каталог, Страница: 71 / 158

4. Capacity and selection data
TCGB0075 rev.0 - 11/2012
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As it is visible in the table, the YUTAKI S80 system that covers the installation’s heating requirements is the combination of
RAS-5HVRNME-AF + RWH-5.0FS(V)NFE. Therefore, this will be the pre-selected YUTAKI S80 system.
N O T E
In case of working with an ambient temperature value not included in the Maximum heating capacity tables of
section Maximum heating capacity tables , (for example, -3 ºC), an interpolation will be needed, using the values
above and below the ambient temperature.
• Step 2: Heating capacity correction for defrost and piping length
The actual heating capacity of the pre-selected unit must be calculated applying the necessary correction factors:
Q
H
= Q
MH
x f
D
x f
LH
Q
H
: Actual heating capacity (kW)
Q
MH
: Maximum heating capacity (kW)
f
D
: Defrost correction factor
f
LH
: Heating piping length correction factor
The maximum heating capacity ( Q
MH
) of the RAS-5H(V)RNME-AF + RWH-5.0FS(V)NFE system is 15.6 kW.
- Calculation of f
D
:
In situations where the ambient temperature is lower than 7 ºC DB,the frost may build up on the heat ex -
changer. In this case, the heating capacity of the system may be reduced because of the time spent by the
system in removing the frost build-up.
The defrosting correction factor takes into account this time and applies the heating capacity correction.
To calculate the correction factor, please see section
Defrost correction factor
which shows a table with
different values of
f
D
depending on the ambient temperature (ºC DB). If the correction factor at an ambient
temperature does not appear on the table, an interpolation will be needed.
Finally, the resulting defrosting correction factor for our outdoor ambient temperature of -10ºC WB is
0.89 .
- Calculation of f
LH
:
Both, the length of the refrigerant piping used and the height difference between the outdoor unit and the
indoor unit, directly affect the unit performance. This concept is quantified by means of the piping length
correction factor.
To determine this value, it is necessary refer to section
Heating piping length correction factor , where it can
be seen the characteristics of this example: equivalent piping length of 20 meters and the indoor unit is
located 15 meters lower than outdoor unit. The resulting piping length correction factor is 0.993.
- Calculation of Q
H
:
Once the correction factors to be applied have been determined, the formula for actual heating capacity of
the RAS-5H(V)RNME-AF + RWH-5.0FS(V)NFE system can be applied:
Q
H
= 15.6 kW x 0.89 x 0.993 = 13.77 kW
As it can be seen, the actual heating capacity of the RAS-5H(V)RNME-AF + RWH-5.0FS(V)NFE system (13.77 kW) is
greater than the heating load required by the installation (13.0 kW). Therefore, the pre-selection will be considered valid.
N O T E
If the actual heating capacity calculated is lower than the required heating load, the calculation must be done
again with the unit immediately above. If there is no unit higher than the pre-selected one, some other system
(combination with boiler or electric heater accessory for example) should be considered.